The present invention relates to methods and apparatuses for measuring the attenuation-versus-frequency characteristics of two-ports (i.e., two-terminal-pair devices), the methods in question being of the type wherein there is applied to the input of the two-port an A.C. voltage which is constant in amplitude but whose frequency is continuously varied using an A.C. voltage generator whose frequency can be electronically controlled using a sawtooth voltage waveform. In methods of this type, the amplitude of the A.C. voltage appearing across the output terminal-pair of the two-port is measured by a digital measuring device, and in one way or another the frequency-dependence of such measured voltage amplitude is ascertained.
The use of a sweep generator or wobbulator to ascertain the frequency response of active and passive two-ports, with the frequency response ascertained being generated upon a display screen, such as of an oscilloscope, results in a complete measuring apparatus which is relatively expensive. Of the information which might be derived from a frequency-response curve thusly displayed on an oscilloscope screen, it will often be the case for various practical applications that only a very small part of the totality of the thusly displayed information, or some simple aspect of it, is actually needed; this is often the case, for example, in routine factory testing and operating measurements with telephone cables. Very often, the only thing actually of interest and to be ascertained from the entire measuring procedure is merely the maximum or minimum value of the attenuation or amplification of the two-port, and an indication of the frequency or frequency range at which such maximum or minimum value occurs.